Interesting RK8E fault

[Josh Dersch]

On Sat, Dec 8, 2018 at 10:33 PM Guy Sotomayor Jr <ggs at shiresoft.com> wrote:

>
> > On Dec 8, 2018, at 8:50 PM, Josh Dersch via cctalk <
> cctalk at classiccmp.org> wrote:
> >
> > On Sat, Dec 8, 2018 at 7:24 PM Paul Anderson via cctalk <
> > cctalk at classiccmp.org> wrote:
> >
> >> Are you using the same pack for the 8 and the 11
> >>
> >
> > I connected the drive I normally use with my 11/40 to the 8/e for testing
> > to help narrow down where the fault was.
> > I used a 16-sector pack in all cases.
>
> You should be using 12 sector packs on the 11 and 16 sector packs on the 8.
>
> I’m actually surprised the 16 sector pack worked on the 11.
>

In all cases /pertinent to this discussion/, i.e. with the RK8E attached to
both the 11/40's RK05 and the RK05 I've restored for the 8/e.

I have 12-sector packs that I normally use with the 11/40.

- Josh






>
> TTFN - Guy
>
> >
> >
> >>
> >> On Sat, Dec 8, 2018 at 8:54 AM Bill Degnan via cctalk <
> >> cctalk at classiccmp.org>
> >> wrote:
> >>
> >>> On Sat, Dec 8, 2018, 1:02 AM Josh Dersch via cctalk <
> >> cctalk at classiccmp.org
> >>> wrote:
> >>>
> >>>> On Fri, Dec 7, 2018 at 9:58 PM Josh Dersch <derschjo at gmail.com>
> wrote:
> >>>>
> >>>>> Hi all --
> >>>>>
> >>>>> Finally got all the parts together (and my act together) to actually
> >>> get
> >>>>> an RK05 lashed up to my PDP-8/e -- only took a decade or so :).  I
> >>> fixed
> >>>> a
> >>>>> few problems with the RK05 and it appears to be behaving very nicely.
> >>>>>
> >>>>> The RK8E controller is mostly working properly but fails
> >> interestingly
> >>>>> when running the formatter, and during the exerciser -- on cylinder
> >> 128
> >>>> and
> >>>>> 192 and very infrequently on cylinder 64 it will get a cylinder
> >>> mismatch
> >>>>> when doing the seek.  When running the formatter during the
> >>> verification
> >>>>> pass, on cyls 64 and 128 if I retry the read it'll continue without
> >>>> issues,
> >>>>> but it's never successful on a retry on cylinder 192.  I tried
> >> hooking
> >>> it
> >>>>> to the RK05 in my 11/40 and it exhibits the same behavior, so I'm
> >>>> guessing
> >>>>> the drive isn't at fault.  And the error is consistent across packs
> >> (of
> >>>>> which I have only two).
> >>>>>
> >>>>> Apart from that fault the drive and controller seem to work fine -- I
> >>>>> wrote out an OS/8 pack with Adventure on it (or at least the first
> >> 191
> >>>>> cylinders of it) and it works without issue.
> >>>>>
> >>>>> Reading the RK8E service docs and schematics, the cylinder address
> >>>> compare
> >>>>> is done by reusing the CRC buffer, so I suspect the issue is in or
> >>> around
> >>>>> there -- the big problem is that debugging it is rather painful since
> >>>> that
> >>>>> logic is in the middle board of a three board set, with jumper blocks
> >>> on
> >>>>> top -- so bringing it out on an extender isn't an option.  I'm
> >> curious
> >>> if
> >>>>> anyone's seen this issue or is so very familiar with the logic that
> >> the
> >>>>> fault is obvious.
> >>>>>
> >>>>> I suspected the 7496 shift register at E14 which takes in the
> >> cylinder
> >>>>> address to be compared w/the header on disk, and I went ahead and
> >>>> replaced
> >>>>> it in the hopes that I'd get lucky, but no go.
> >>>>>
> >>>>> Anyone have any advice?
> >>>>>
> >>>>> Thanks,
> >>>>> Josh
> >>>>>
> >>>>>
> >>>> I'll add that during the format/verification the drive seeks properly
> >>> (i.e.
> >>>> it's not missing a step or overstepping), which I've confirmed by
> >>> watching
> >>>> the thing walk through the tracks with the cover off.
> >>>>
> >>>> - Josh
> >>>>
> >>>
> >>> Partitions as rka0 / rka1?
> >>> B
> >>>
> >>>>
> >>>
> >>
>
>